PHILADELPHIA (CBS) — In honor of the 306th anniversary of Benjamin Franklin’s birth today, park rangers from Independence National Historical Park were demonstrating one of Dr. Franklin’s inventions at the visitors’ center at 6th and Market Streets.

With damp fingers, park ranger Tom Degnan (back to camera in photo) was playing a glass armonica, a musical instrument invented by Benjamin Franklin in 1761.

Degnan says Franklin was inspired by a concert he attended in which the music was made from tones produced by running a finger around the rims of wine glasses filled with water to different levels.

“And he loved the sound that he heard — he thought it was heavenly,” Degnan tells KYW Newsradio. “But he though there was a better way to do it, and that was to arrange bowls one inside the other and there would be a spindle running through all the bowls so, when the spindle turned, all the bowls would turn.”